Golf club

ABSTRACT

The golf club includes a shaft, a golf club head equipped with a face portion and a hosel portion having an attachment hole for insertion of the shaft, and a support member attached to an opening portion of the attachment hole and formed into a cylindrical shape covering the outer circumferential surface of the shaft. The shaft includes a hollow shaft body and a sheet-like reinforcing layer constituted by low-elasticity fibers and arranged in the shaft body, the reinforcing layer being arranged at a position corresponding to at least the support member. The attachment hole includes a support portion having an inner diameter for supporting the outer circumferential surface of the shaft, and an engaging portion continuous with the support portion, having a larger inner diameter than the support portion, and open to the outside in an opening of the attachment hole.

This application claims priorities to Japanese Patent Applications No. 2014-134762 filed on Jun. 30, 2014, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a golf club.

BACKGROUND ART

In recent years, there has been a trend of weight reduction in the shafts of wood-type golf clubs as described in JP 2008-264345A, and among such trends there has been a proposal to arrange the center of gravity of the shaft on the grip side in order to facilitate swinging.

SUMMARY OF INVENTION

However, if the center of gravity of the shaft is arranged on the grip side in addition to a weight reduction, the thickness of the shaft on the head side decreases, and there is a risk of a decrease in strength. Due to the decrease in strength, there is a problem of breakage of the shaft in the coupling portion between the head and the shaft, that is to say in the vicinity of the hosel portion. For example, since there is large variation in the ball impact point with an average golfer, there are cases where the ball is hit by a portion in the vicinity of the hosel portion, and in this case there is a possibility of the shaft breaking with one hit.

The present invention has been achieved in order to solve the above problems, and an object thereof is to provide a golf club that enables improving the strength in the coupling portion between the shaft and the hosel portion while maintaining a reduction in the weight of the shaft.

A golf club according to the present invention includes: a shaft; a golf club head equipped with a face portion and a hosel portion having an attachment hole for insertion of the shaft; and a support member attached to an opening portion of the attachment hole and formed into a cylindrical shape covering an outer circumferential surface of the shaft, wherein the shaft includes a hollow shaft body formed by stacking a plurality of sheet-like layers, and a sheet-like reinforcing layer constituted by low-elasticity fibers and arranged radially inward of a thickness center of the shaft body, the reinforcing layer being arranged at a position corresponding to at least the support member, the attachment hole includes a support portion having an inner diameter for supporting the outer circumferential surface of the shaft, and an engaging portion continuous with the support portion, having a larger inner diameter than the support portion, and open to the outside in an opening of the attachment hole, and the support member includes a ring-shaped inner portion configured to be fitted into the engaging portion of the attachment hole, and a ring-shaped outer portion configured to be coupled to the inner portion and come into contact with a peripheral edge of the opening of the attachment hole.

In the above golf club, the reinforcing layer may be formed using carbon fibers or glass fibers, and have a tensile modulus of 20 ton/mm² or less.

In the above golf club, the reinforcing layer may be arranged at an inner circumferential surface of the shaft body.

In the above golf club, the hosel portion may be formed using a metal material, and the support member may be formed using a resin material.

In the above golf club, the engaging portion of the attachment hole may be formed into a tapered shape whose inner diameter increases as the engaging portion extends to an opening side of the attachment hole, and the inner portion of the support member may be formed into a tapered shape whose outer diameter decreases as the inner portion extends away from the outer portion in an axial direction, so as to correspond to the engaging portion.

According to the present invention, it is possible to improve the strength in the coupling portion between the shaft and the hosel portion while maintaining a reduction in the weight of the shaft.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a reference state in one embodiment of a golf club according to the present invention;

FIG. 2 is a plan view of a golf club head in FIG. 1;

FIG. 3 is a development diagram (sheet constitution diagram) of prepreg sheets constituting a shaft of the golf club in FIG. 1;

FIG. 4 is a cross-sectional view of a vicinity of a hosel portion of the golf club in FIG. 1;

FIG. 5 is a cross-sectional view showing another example of a support member and the hosel portion of the golf club in FIG. 1;

FIG. 6 is a cross-sectional view showing another example of a vicinity of the hosel portion of the golf club according to the present invention; and

FIG. 7 is a cross-sectional view of a support member according to a working example.

DESCRIPTION OF EMBODIMENTS

An embodiment of a golf club head according to the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of a reference state of the golf club of the present embodiment, and FIG. 2 is a plan view of the golf club head in FIG. 1. Note that the reference state of the golf club will be described later.

1. Overview of Golf Club

As shown in FIGS. 1 and 2, the golf club of the present embodiment is a wood-type golf club that includes a golf club head (hereinafter sometimes simply referred to as the “head” or the “club head”) 1 and a shaft 2 coupled thereto, and a cylindrical support member 5 is furthermore attached to a coupling portion between the head and the shaft. These members will be described in detail below.

1-1. Overview of Head Body

As shown in FIGS. 1 and 2, the head 1 of the present embodiment is a hollow structure and has wall surfaces formed by a face portion 11, a crown portion 12, a sole portion 13, a side portion 14, and a hosel portion 15. The face portion 11 has a face surface, which is the surface for hitting a ball, and the crown portion 12 is adjacent to the face portion 11 and constitutes the upper surface of the head. The sole portion 13 constitutes the bottom surface of the head 1, and is adjacent to the face portion 11 and the side portion 14. Also, the side portion 14 is the portion between the crown portion 12 and the sole portion 13, and extends from the toe side of the face portion 11, across the back side of the head 1, to the heel side of the face portion 11. Furthermore, the hosel portion 15 is a cylindrical portion provided adjacent to the heel side of the crown portion 12, and has an attachment hole 151 for the insertion of the shaft 2 of the golf club. A central axis Z of the attachment hole 151 conforms to the axis of the shaft 2.

The following describes the aforementioned reference state. First, as shown in FIGS. 1 and 2, the reference state is defined as a state in which the central axis Z is in a plane P1 that is perpendicular to the ground (horizontal plane), and furthermore the head is placed on the ground at a predetermined lie angle and real loft angle. The plane P1 will be referred to as the reference vertical plane. Also, as shown in FIG. 2, the direction of the line of intersection of the reference vertical plane P1 and the ground will be referred to as the toe-heel direction, and the direction that is perpendicular to the toe-heel direction and parallel to the ground will be referred to as the face-back direction.

In the present embodiment, the boundary between the sole portion 13 and the face portion 11, and the boundary between the sole portion 13 and the side portion 14 can be defined as follows. Specifically, if ridge lines are formed between the sole portion 13 and the face portion 11, and between the sole portion 13 and the side portion 14, those ridge lines serve as the boundaries. Also, although the head 1 of the present embodiment has the side portion 14, in the case where the side portion 14 is not provided, and the sole portion 13 and the crown portion 12 are directly connected for example, the ridge line between the sole portion 13 and the crown portion 12 serves as the boundary between the two. Also, if a clear ridge line is not formed, the boundary is the outline that is seen when the head 1 is placed in the reference state and viewed from directly above the center of gravity of the head body.

Note that although an upper limit is not particularly defined for the volume of the head body 1, practically it is, for example, desirably 500 cm³ or less, or desirably 470 cm³ or less when complying with R&A or USGA rules and regulations.

Also, the head 1 can be formed from a metal material such as a titanium alloy having a specific gravity of approximately 4.4 to 4.5 (Ti-6Al-4V). Besides a titanium alloy, the head can be formed from one or two or more materials selected from among stainless steel, maraging steel, an aluminum alloy, a magnesium alloy, an amorphous alloy, and the like.

Note that the head 1 of the present embodiment is constituted by combining a head body that has at least the sole portion 13 with another portion. For example, a configuration is possible in which only the face portion 11 is constituted by another member, and the head is constituted by attaching the face portion 11 to the head structure body, and it is also possible to constitute a head 1 by forming a head body in which an opening is provided in the crown portion 12 and the side portion 14, and blocking the opening with another member.

1-2. Shaft

Next, the shaft will be described. The term “layer” and the term “sheet” are used in the following description. The term “layer” is used after wrapping, whereas the term “sheet” is used before wrapping. A “layer” is formed due to a “sheet” being wrapped. In other words, a wrapped “sheet” forms a “layer”. Also, in the following description, “inner” means being inward in the shaft diameter direction, and “outer” means being outward in the shaft diameter direction.

The shaft 2 is a so-called carbon shaft constituted by stacked body including multiple fiber-reinforced resin layers, and has a hollow structure. One end portion of this shaft is fixed to the hosel portion 15 of the head 1, and the other end portion is attached to a grip 7. Here, the side located inside the head 1 is referred to as the tip Tp, and the side located inside the grip is referred to as the butt Bt.

The shaft 2 is formed by allowing prepreg sheets to cure, for example. In the prepreg sheets, fibers are aligned in substantially the same direction. A prepreg in which the fibers are aligned in substantially the same direction in this way is also referred to as a UD prepreg. “UD” is an abbreviation for unidirectional. Note that a prepreg other than a UD prepreg may be used. For example, the fibers contained in the prepreg sheet may be woven.

Also, it is preferable that the prepreg sheets have fibers and resin. The fibers can be glass fibers or carbon fibers, for example. A glass fiber reinforced prepreg can be used as the prepreg, for example. This glass fiber reinforced prepreg is a prepreg in which the reinforcing fibers are glass fibers. Besides a glass fiber reinforced prepreg, a carbon fiber reinforced prepreg can be used. Examples of carbon fibers include PAN-based and pitch-based fibers. Also, as will be described later, it is preferable that on the tip side of the shaft 2, the prepreg sheet arranged as the innermost layer (the later-described first sheet s1) is constituted by low-elasticity fibers. Specifically, it is preferable that the tensile modulus is 20 ton/mm² or less, and more preferably 15 ton/mm² or less. Also, it is preferable that the tensile modulus of the other prepreg sheets is 22 to 90 ton/mm².

On the other hand, the resin is referred to as a matrix resin, which can be formed by a thermosetting resin, for example. Examples of the matrix resin can include not only an epoxy resin, but also a thermosetting resin other than an epoxy resin, and a thermoplastic resin. From the viewpoint of shaft strength, it is preferable that the matrix resin is an epoxy resin.

Next, the sheets constituting the shaft 2 will be described in further detail. The shaft 2 can be manufactured using a so-called sheet winding method, for example. First, the matrix resin in the prepregs is put in a semi-cured state. Then the shaft 2 is formed by winding the prepreg sheets and allowing them to cure. This “curing” means allowing the matrix resin in the semi-cured state to cure, and is achieved by heating. For this reason, a heating step is included among the steps for manufacturing the shaft 2. The matrix resin in the prepreg sheets cures due to this heating step.

FIG. 3 is a development diagram (sheet constitution diagram) of prepreg sheets constituting the shaft 2. As shown in this figure, the shaft 2 is constituted by multiple sheets. In this example, the shaft 2 is constituted by eight sheets, namely a first sheet s1 to an eighth sheet s8. Note that in the development diagram shown in FIG. 3, the sheets constituting the shaft 2 are shown in order from the inner side in the radial direction of the shaft. In other words, winding is performed beginning with the sheet located at the top in the development diagram. Also, in this development diagram, the left-right direction in the diagram conforms to the shaft axial direction. Accordingly, in this development diagram, the right side of the diagram is the tip Tp side of the shaft 2, and the left side is the butt Bt side of the shaft 2.

Furthermore, in this development diagram, the sheets are arranged not only in the sheet winding order, but also in the shaft axial direction. For example, the right end of the first sheet s1 is located at the tip Tp in FIG. 3.

Also, a layer s2, a layer s3, a layer s5, a layer s6, and a layer s7 formed by the second, third, fifth, sixth, and seventh sheets are arranged over approximately the entire length of the shaft 2, and a layer s1, a layer s4, and a layer s8 formed by the first, fourth, and eighth sheets are arranged in portions of the shaft 2. Specifically, the layer s1 and the layer s8 constituted by the first and eighth sheets are arranged on the tip Tp side of the shaft 2, and the layer s4 constituted by the fourth sheet is arranged on the butt Bt of the shaft 2.

In FIG. 3, double-sided arrows Lt1 and Lt2 respectively indicate the length between the rear end of the layer s1 and the tip end Tp of the shaft 2 and the length between the rear end of the layer s8 and the tip end Tp of the shaft 2. From the viewpoint of reinforcing the tip portion while suppressing the shaft weight, the distance Lt is preferably 400 mm or less, more preferably 350 mm or less, and further preferably 300 mm or less. In particular, these lengths Lt1 and Lt2 need to correspond to the later-described support member 5.

On the other hand, a double-sided arrow Lb in FIG. 3 indicates the distance between the tip of the layer s4 and the butt end Bt of the shaft 2. From the viewpoint of arranging the center of gravity of the shaft on the grip side while suppressing the shaft weight, the distance Lb is preferably 500 mm or less, more preferably 450 mm or less, and further preferably 400 mm or less.

Although there are no particular limitations on the thickness of the prepreg sheets, the thickness of the layer s1, which is constituted by low-elasticity fibers, can be set to 0.1 to 0.5 mm, and the thickness of the other layers can be set to 2.0 to 3.9 mm, for example. Note that the total thickness of all of the layers is preferably 2.5 to 4.0 mm.

Also, the first sheet s1 to eighth sheet s8 constituting the shaft 2 can be classified into straight layers, bias layers, and hoop layers according to differences in the fiber alignment direction. For example, the alignment direction angles of the fibers are indicated in the development diagram of FIG. 3, and a sheet marked with “0° ” constitutes a straight layer. A sheet for a straight layer is also called a straight sheet.

A straight layer is a layer in which the alignment direction of the fibers is substantially 0° relative to the lengthwise direction of the shaft (shaft axial direction). Normally, the alignment direction of the fibers is not completely parallel with the shaft axis line direction due to error during winding or the like. For this reason, an absolute angle θa of the fibers relative to the shaft axis line is 10° or less in the straight layer. The absolute angle θa is the absolute value of the angle formed by the shaft axis line and the fiber direction. In other words, if the absolute angle θa is 10° or less, this means that an angle Af formed by the fiber direction and the shaft axis line direction is in the range of −10 degrees to +10 degrees inclusive.

In the example in FIG. 3, the straight sheets are the sheet s1, the sheet s4, the sheet s5, the sheet s7, and the sheet s8. In a straight layer, there is a high correlation between bending rigidity and bending strength.

Next, the bias layer will be described. The bias layer is provided mainly for the purpose of raising the twist rigidity and the twist strength of the shaft. It is preferable that the bias layer is constituted by a pair of two sheets in which the fiber alignment directions are inclined in mutually opposite directions. It is preferable that the bias layer includes a layer whose angle Af is in the range of −60° to −30° inclusive, and a layer whose angle Af is in the range of 30° to 60° inclusive. In other words, it is preferable that the absolute angle θa is in the range of 30° to 60° inclusive in the bias layer.

In the shaft 2, the sheets constituting the bias layer are the sheet s2 and the sheet s3. In FIG. 3, the angle Af is indicated for each sheet. The plus (+) and minus (−) signs in the angles Af indicate that the fibers in the bias sheets that are to be fixed together are inclined in mutually opposite directions. Also, sheets for the bias layer are also referred to as simply bias sheets. Note that although −45 degrees is indicated for the sheet s2 and +45 degrees is indicated for the sheet s3 in the embodiment shown in FIG. 3, it is of course possible for, conversely, the sheet s2 to have an angle of +45 degrees and the sheet s3 to have an angle of −45 degrees.

Next, the hoop layer will be described. A hoop layer is a layer in which the fibers are aligned in the circumferential direction of the shaft. It is preferable that the absolute angle θa of the hoop layer is substantially 90° relative to the shaft axis line. Note that there are cases where the alignment direction of the fibers is not completely 90° relative to the shaft axis line direction due to error during winding or the like. Normally, the absolute angle θa is 80° or more in the hoop layer. The upper limit value of the absolute angle θa is 90°.

The hoop layer contributes to an increase in the crush rigidity and crush strength of the shaft. Crush rigidity refers to rigidity with respect to the force crushing the shaft inward in the radial direction. On the other hand, crush strength refers to strength with respect to the force crushing the shaft inward in the radial direction. The crush strength can be correlated with the bending strength as well. Also, crush deformation can occur in conjunction with bending deformation. In particular, this relationship is strong with a thin and light-weight shaft. Accordingly, the bending strength can be improved by improving the crush strength.

In the example in FIG. 3, the prepreg sheet for the hoop layer is the first sheet s6. The prepreg sheet for the hoop layer is also called a hoop sheet.

The above-described prepreg sheets are sandwiched between cover sheets before being used. Normally, the cover sheets are a release paper and a resin film, and the prepreg sheets are sandwiched by the release paper and the resin film. More specifically, the release paper is affixed to one surface of the prepreg sheets, and the resin film is affixed to the other surface of the prepreg sheets. Accordingly, in the following description, the surface to which the release paper is affixed is referred to as the “release paper-side surface”, and the surface to which the resin film is affixed is referred to as the “film-side surface”.

Note that the following shows one example of specifications of the prepreg sheets in FIG. 3.

TABLE 1 Tensile Thick- Fiber Resin Prepreg modulus ness FAW percentage FAW Material (ton/mm²) (mm) (g/m²) (%) (g/m²) 1st Glass fiber 7 0.15 160 35 246 sheet Epoxy resin s1 2nd Carbon fiber 40 0.06 70 25 93 sheet Epoxy resin s2 3rd Carbon fiber 40 0.06 70 25 93 sheet Epoxy resin s3 4th Carbon fiber 24 0.1 125 25 167 sheet Epoxy resin s4 5th Carbon fiber 24 0.08 100 25 133 sheet Epoxy resin s5 6th Carbon fiber 30 0.03 30 40 50 sheet Epoxy resin s6 7th Carbon fiber 24 0.17 175 25 233 sheet Epoxy resin s7 8th Carbon fiber 24 0.08 100 25 133 sheet Epoxy resin s8 Note: (FAW: Fiber Areal Weight)

Next, the method for winding the prepreg sheets will be described. In order to wind the prepreg sheets, first the resin film is removed. Removing the resin film exposes the film-side surface. This exposed surface has stickiness (adhesiveness). This stickiness is due to the matrix resin. In other words, adhesiveness appears due to the matrix resin being in the semi-cured state. Next, the edge portion of the exposed film-side surface (also called the winding start edge portion) is affixed to the winding target object. Due to the adhesiveness of the matrix resin, the winding start edge portion can be affixed smoothly. The winding target object is a mandrel or a winding object obtained by winding another prepreg sheet around a mandrel.

Next, the release paper is removed. The winding target object is then rotated such that the prepreg sheet is wound around the winding target object. In this way, first the resin film is removed, then the winding start end portion is affixed to the winding target object, and then the release paper is removed. This procedure suppresses sheet wrinkling and winding failures. This is because the sheet with the release paper affixed thereto is supported by the release paper, thus suppressing wrinkling. This is also due to the fact that the release paper has a higher bending rigidity than the resin film.

An integrated sheet is used in the example in FIG. 3. An integrated sheet is formed by affixing two sheets together.

In the embodiment shown in FIG. 3, one integrated sheet is formed. This integrated sheet is formed as a bias integrated sheet in which the sheet s3 and the sheet s4 are affixed to each other. The two sheets s3 and s4 whose fiber alignment direction angles are opposite to each other are used as the bias layer. This set of the sheets s3 and s4 makes it possible to eliminate a directional characteristic in the twisting direction. The bias integrated sheet is used for this purpose.

1-3. Hosel Portion and Support Member

Next, the hosel portion 15 and the support member 5 will be described with reference to FIG. 4. FIG. 4 is a cross-sectional view of the vicinity of the hosel portion. As described above, the hosel portion 15 is formed into a cylindrical shape, and is provided with the attachment hole 151 for insertion of the shaft 2. As shown in FIG. 4, the attachment hole 151 is constituted by two portions having different inner diameters. Specifically, the attachment hole 151 is constituted by a support portion 153 that has approximately the same inner diameter as the outer diameter of the shaft 2, and an engaging portion 154 that is concentrically continuous with the support portion 153 and has a larger inner diameter than the support portion 153. A level difference is formed at the boundary between the support portion 153 and the engaging portion 154. The engaging portion 154 is arranged on the opening side of the attachment hole 151, and is open to the outside.

Next, the support member 5 will be described. The support member 5 is attached to the upper end portion of the hosel portion 15. As shown in FIG. 4, the support member 5 includes an outer portion 31 and an inner portion 32 that are formed into a cylindrical shape, and these two portions are formed integrally. The outer portion 31 is a portion that is exposed to the outside from the upper end portion of the hosel portion 15, and the inner portion 32 is a portion that is arranged inside the attachment hole 151 of the hosel portion 15 and cannot be seen from the outside.

The outer circumferential surface of the outer portion 31 is formed into a tapered shape whose diameter decreases from the lower end portion toward the upper end portion, and the outer diameter of the lower end portion is approximately the same as the outer diameter of the upper end portion of the hosel portion 15. Also, the interior space of the outer portion 31 is formed into a cylindrical shape whose inner diameter is approximately the same as the outer diameter of the shaft 2. On the other hand, the inner portion 32 has an outer diameter approximately the same as the inner diameter of the engaging portion 154 in the attachment hole 151 of the hosel portion 15, and is formed so as to fit into the engaging portion 154. Also, the interior space of the inner portion 32 is formed into a cylindrical shape that is continuous with and has the same diameter as the interior space of the outer portion 31. It is preferable that a length t of the inner portion 32 in the axial direction is 3 to 7 mm, for example, in order to improve a later-described impact mitigating effect. Also, the layer thickness of the inner portion 32 can be set to 0.2 to 1.0 mm, for example.

Although the support member 5 can be formed using a metal, a resin, or the like, it is preferably formed using a material that is lighter-weight and more flexible than to the hosel portion 15 and the shaft 2. For example, it can be formed using acetylcellulose. Also, the support member 5 may be formed so as to also be able to be used as a ring-shaped decorative member that is called a socket, ferrule, or the like and is ordinarily attached to the shaft 2.

2. Features

Effects such as the following can be obtained by the present embodiment. First, the layer s1 containing low-elasticity fibers is arranged as the innermost layer in the portion of the shaft 2 in the vicinity of the hosel portion 15. The tensile modulus of the layer s1 is 20 ton/mm² or less, and thus is low-elasticity. This point will be described below in detail. First, the bending rigidity and the like of the shaft are influenced by the characteristics of the layer arranged on the outer side among the layers constituting the shaft. In view of this, in the present embodiment, impact strength is improved by arranging low-elasticity fibers in the layer on the inner side that has little contribution to the bending rigidity. In comparison with the case of using a high-elasticity layer as the inner layer of the shaft 2, using the low-elasticity layer s1 as the inner layer reduces the bending rigidity in no small measure. However, this facilitates flexure in the tip portion of the shaft 2. If the tip portion of the shaft flexes easily in this way, impact is mitigated when the ball is hit with a portion in the vicinity of the hosel portion 15. Furthermore, although the shaft 2 flexes when the ball is hit with a portion in the vicinity of the hosel portion 15, the shaft 2 is supported by the inner portion 32 of the support member 5 at this time. The inner portion 32 is more flexible than the shaft 2 and the hosel portion 15, and therefore serves as cushioning.

Also, since the inner layer of the shaft has little contribution to the bending rigidity, arranging the low-elasticity fiber layer on the inner layer side makes it possible to form a relatively thick low-elasticity layer as this layer, and an improvement in impact absorption is also inferred.

Furthermore, a level difference (level difference at the boundary between the support portion 153 and the engaging portion 154) is formed in the hosel portion 15, and providing the support member configured as described above also obtains advantages such as the following. A comparison with a conventional support member will be given with respect to this point. For example, when hitting a ball with the hosel portion 15, in the case of a conventional golf club in which a level difference is not provided in the hosel portion 15, and in which the shaft 2 is constricted in the hosel portion 15 as shown in (a) of FIG. 5, the shaft 2 starts to bend at the upper end of the hosel portion 15 (point A), and stress becomes concentrated in this portion. As a result, a tendency for shaft breakage to occur in the vicinity of the point A is inferred.

In contrast, in the present embodiment, the upper end of the portion of the shaft 2 constricted in the hosel portion 15 is at the lower end of the engaging portion 154 (point B), and stress becomes concentrated a lower position than in conventional golf clubs. Also, the axial-direction length of the support member arranged above the point at which stress becomes concentrated is longer in the support member 5 of the present embodiment (L1) than in a support member 50 of the comparative example (L2). Accordingly, in the present embodiment, the support member 5 that serves as cushioning has a long length, thus suppressing bending of the shaft 2, which consequently enables preventing breakage of the shaft 2.

Also, the shaft 2 is in contact with the lower end of the level difference in the hosel portion 15, and is in contact with the hosel portion 15 in a manner in which bending of the shaft 2 is elastically supported by the inner portion 32 of the support member 5. Since the hosel portion 15 is hard, stress becomes concentrated in the shaft 2 at the point of contact with the hosel portion 15, but due to the shaft 2 being in contact with the hosel portion 15 in a manner in which bending of the shaft 2 is elastically supported, this stress is mitigated, and it is thought to be possible to suppress breakage of the shaft. Accordingly, it is possible to improve impact strength while relatively suppressing a decrease in the bending rigidity.

Furthermore, since the engaging portion 154 is formed in the attachment hole 151 of the hosel portion 15, effects such as the following can be obtained. Specifically, the hosel portion 15 is normally formed using a metal, and a portion thereof is cut away to form the engaging portion 154. Then the inner portion 32 of the support member 5, which is formed using a resin, is arranged in the engaging portion 154. Accordingly, in the hosel portion 15, a metal portion having a high specific gravity is cut away, and resin having a low specific gravity is arranged in this portion, and therefore the upper portion of the hosel portion 15, that is to say the upper portion of the head 1, has a small specific gravity. As a result, it is possible to relatively lower the center of gravity of the head 1.

As described above, according to the present embodiment, the layer s1 formed using low-elasticity fibers is arranged as the innermost layer of the shaft 2, thus making it possible to prevent a decrease in the bending rigidity. Also, the above-described support member 5 is arranged at a position corresponding to the layer s1, thus improving cushioning performance when a ball is hit with the hosel portion 15. Accordingly, it is possible to improve strength against impact.

5. Variations

Although an embodiment of the present invention has been described above, the present invention is not limited to this embodiment, and various modifications can be made without departing from the gist of the invention. The following are examples of modifications that can be made.

5.1 There are no particular limitations on the shape of the support member 5, and a configuration is possible in which, for example, the outer circumferential surface of the outer portion 31 is not given a tapered shape, but rather given a cylindrical shape having a constant outer diameter. Alternatively, the outer shape may be a polygonal shape. Also, there are no particular limitations on the shape of the inner portion 32 either, and it may have a shape for engaging with the engaging portion 154 of the hosel portion 15. For example, as shown in FIG. 6, a configuration is possible in which the inner portion 32 is formed into a tapered shape whose outer diameter decreases as it extends downward, and the inner wall of the engaging portion 154 of the attachment hole 151 of the hosel portion 15 is formed into a corresponding tapered shape whose inner diameter decreases as it extends downward. This facilitates attachment of the support member 5 to the hosel portion 15. Furthermore, assembly workability is improved.

5.2

The shaft of the above embodiment is one example, there are no particular limitations on the materials and shapes of the sheets and the layers, and the number of sheets can be changed as appropriate. Note that the first sheet (layer s1) of the above embodiment corresponds to the reinforcing layer of the present invention, and the layers s2 to s8 constituted by the other second to eighth sheets correspond to the shaft body of the present invention. Also, although the reinforcing layer is arranged as the innermost layer of the shaft 2 in the above embodiment, the reinforcing layer need only be arranged radially inward of the thickness center of the shaft body constituted by the layers other than the reinforcing layer.

5.3

Although a wood-type golf club head is described in the above embodiment, the golf club head of the present invention can be applied to a so-called iron-type, utility-type, or hybrid-type golf club head as well.

Working Examples

The following describes working examples of the present invention. Note that the present invention is not limited to the following working examples.

Working Examples 1 to 8 (WE1 to WE8) and Comparative Examples 1 to 4 (CE1 to CE4) having different support members and reinforcing layers were subjected to a test regarding the strength of the shaft. A #1 wood (volume of 460 cm³) was used as the golf club. The shape of the support member was as shown in FIG. 7, and the dimensions are shown in Table 2 below. Note that the lengths t of the inner portion in the axial direction were different between the working examples and the comparative examples as shown in Table 3.

TABLE 2 Length Outer diameter A of upper end of outer portion 11.3 mm  Outer diameter B of lower end of outer portion 13.8 mm  Axial length C of outer portion 7.0 mm Outer diameter D of inner portion 9.8 mm Inner diameter E of internal space of support member 8.8 mm

TABLE 3 WE 1 WE 2 WE 3 WE 4 WE 5 WE 6 WE 7 WE 8 CE 1 CE 2 CE 3 CE 4 Axial 1 3 5 7 1 3 5 7 1 3 5 7 length t of inner portion (mm)

Also, the shafts in the working examples and the comparative examples were constituted as described below. First, in Working Examples 1 to 4, the shafts were as shown in FIG. 3 and Table 1. Here, the sheets arranged as the layers s1 to s8 are indicated as sheets a to h. In contrast, in Working Examples 5 to 8, the sheet a formed using low-elasticity fibers was arranged between the layer s2 and the layer s4. Also, in the comparative examples, a sheet a′ formed using high-elasticity fibers instead of the sheet a was arranged as the layer s1. Details of this are shown in Table 4. Also, the characteristics of the sheet a′, the shape of the shaft, and the like are shown in Table 5.

TABLE 4 Working Working Comparative Examples 1-4 Examples 5-8 Examples 1-4 Layer s1 a (low-elasticity b a′ (high-elasticity fibers) fibers) Layer s2 b c b Layer s3 c a (low-elasticity c fibers) Layer s4 d d d Layer s5 e e e Layer s6 f f f Layer s7 g g g Layer s8 h h h

TABLE 5 Length Shaft outer diameter: tip end 9.0 mm Shaft outer diameter: butt end 16.0 mm Shaft inner diameter: tip end 6.0 mm Shaft inner diameter: butt end 14.0 mm Shaft length 46 inches (1168 mm) Shaft length in hosel portion 38 mm Sheet a′ material in CE Carbon fibers + epoxy resin Sheet a′ thickness in CE 0.15 mm Sheet a′ fiber FAW in CE 175 g/m² Sheet a′ resin % in CE 30% Sheet a′ prepreg FAW in CE 250 g/m²

The working examples and comparative examples described above were prepared, and a test was performed by using a swinging machine to hit balls with the hosel portion. Specifically, the head speed (H/S) was raised by 2 m/s each time from 20 m/s, and the head speed at which the shaft broke was recorded. The results were as follows.

TABLE 6 WE 1 WE 2 WE 3 WE 4 WE 5 WE 6 WE 7 WE 8 CE 1 CE 2 CE 3 CE 4 Shaft 28 36 40 38 26 32 34 34 20 22 24 24 break speed H/S (m/s)

According to Table 6, the longer the length of the inner portion in the axial direction was, the better the durability of the shaft was maintained even with a high head speed. Also, it was found that durability was improved when the layer formed using low-elasticity fibers was provided as the innermost layer of the shaft or radially inward of the thickness center of the shaft (more specifically, radially inward of the thickness center of the shaft body constituted by the layers other than the layer formed using low-elasticity fibers). On the other hand, it was found that if a layer formed using low-elasticity fibers was not provided, as in the comparative examples, the shaft broke even with a low head speed.

REFERENCE SIGNS LIST

-   -   1 Head     -   2 Shaft     -   5 Support member     -   11 Face portion     -   15 Hosel portion     -   31 Outer portion     -   32 Inner portion     -   50 Support member     -   151 Attachment hole     -   153 Support portion     -   154 Engaging portion 

1. A golf club comprising: a shaft; a golf club head equipped with a face portion and a hosel portion having an attachment hole for insertion of the shaft; and a support member attached to an opening portion of the attachment hole and formed into a cylindrical shape covering an outer circumferential surface of the shaft, wherein the shaft includes a hollow shaft body formed by stacking a plurality of sheet-like layers, and a sheet-like reinforcing layer constituted by low-elasticity fibers and arranged radially inward of a thickness center of the shaft body, the reinforcing layer being arranged at a position corresponding to at least the support member, the attachment hole includes a support portion having an inner diameter for supporting the outer circumferential surface of the shaft, and an engaging portion continuous with the support portion, having a larger inner diameter than the support portion, and open to the outside in an opening of the attachment hole, and the support member includes a ring-shaped inner portion configured to be fitted into the engaging portion of the attachment hole, and a ring-shaped outer portion configured to be coupled to the inner portion and come into contact with a peripheral edge of the opening of the attachment hole.
 2. The golf club according to claim 1, wherein the reinforcing layer is formed using carbon fibers or glass fibers, and has a tensile modulus of 20 ton/mm² or less.
 3. The golf club according to claim 1, wherein the reinforcing layer is arranged at an inner circumferential surface of the shaft body.
 4. The golf club according to claim 1, wherein the hosel portion is formed using a metal material, and the support member is formed using a resin material.
 5. The golf club according to claim 1, wherein the engaging portion of the attachment hole is formed into a tapered shape whose inner diameter increases as the engaging portion extends to an opening side of the attachment hole, and the inner portion of the support member is formed into a tapered shape whose outer diameter decreases as the inner portion extends away from the outer portion in an axial direction, so as to correspond to the engaging portion. 